1. Field of the Invention
The present invention relates generally to random number generators and particularly to random number generators with a ring oscillation circuit.
2. Description of the Background Art
In the field of information security it is essential to use random numbers and in recent years there is an increasing demand for high-performance random number generators generating true random numbers, natural random numbers that have uniformity (i.e., are identical in probability in value and frequency of appearance) and appear without ordinality, relevance with preceding and following numbers, or periodicity. One such random number generator employs a random pulse obtained by utilizing weak radioactive rays, resistors, diodes and other similar elements' thermal noise, crystal oscillators' fluctuations, and other similar natural phenomena.
In a conventional random number generator a flip-flop generating a random number has an input line with a jitter generation circuit added thereto so as to utilize an input signal's jitter to allow the flip-flop to provide an output having an increased range of indeterministic operation, as proposed for example in Japanese Patent Laying-Open No. 2002-366347.
Furthermore, a substrate effect of a field effect transistor configuring a ring oscillation circuit is utilized to vary the ring oscillation circuit's oscillation frequency to generate a clock signal varying in frequency, and the clock signal's pulses are counted by a counter to generate a random number, as described for example in Japanese Patent Laying-Open No. 2001-331306.
Random number generators utilizing random pulses attributed to natural phenomena, however, include a random pulse generation source, a signal amplifier, a waveform shaping circuit, a uniformity optimization circuit and other similar analog elements and as a result would have increased circuit scales and also be complicated. This is an obstacle to mounting these elements as an integrated large scale integrated circuit (LSI) on microcomputers, application specific integrated circuits (ASICs) and the like. In addition, those utilizing thermal noise are susceptible to external noise and the like and thus operate less reliably. Those utilizing radioactive rays may have negative effect on environments.
For application to ultra-compact and thin, high-technology equipment, random number generators further miniaturized and having reduced power consumption, and of high performance are required.